Molecular machines, such as the ribosome or the nuclear pore, are of critical importance for the smooth functioning of the cell. This proposal deals with two issues that are important for the construction of ANY molecular machine, but are particularly acute for the ribosome: (A) How to supply the right amount of each of the constituent molecules, and (B) How to exert quality control over the final product and dispose of those complexes that do not meet standards. For S. cerevisiae construction of the ribosome consumes a major portion of its economy;effective ribosome synthesis is critical for its fitness. For mammalian organisms the construction of the ribosome is closely monitored as a measure of the cell's health;aberrant ribosome synthesis leads to cell cycle arrest or cell death, and has been implicated in several disease states. We have identified a complex of four proteins that appears to be a key factor in coupling the synthesis of ribosomal RNA and ribosomal proteins. We are proposing experiments to confirm this connection and to try to identify the biochemical and physiological basis for this coupling. We have developed a system in which there is a major and chronic, but not lethal, accumulation of aberrant pre-ribosomes of various types. We will use this system in both genetic and biochemical experiments to discover the genes and the biochemistry behind the identification and degradation of such aberrant pre-ribosomes. Preliminary data suggests the involvement of a rather unusual set of several distinct members of the ubiquitin-proteasome system, as well as some members of the TRAMP-exosome complex. The success of these experiments will provide new insight into how a cell can maintain BALANCE in the production of the components of a molecular machine, as well as how the cell can dispose of aberrant ribosomes at least risk to itself.